Default group required

* adds access checks depending on the current group confgiguration of a user
* removes buttons for adding/editing or removing data if default group is not set for a user
* removes buttons for adding/removing related data in unshared interventions
* removes shared-user setting from share menu of an intervention if user is not zb or ets
* renames has_access() from intervention Model into is_shared_with() for more clarity
* fixes bug in group check in_group() from utils.py

intervention/models.py

@@ -207,7 +207,7 @@ class Intervention(BaseObject):
             self.identifier = new_id
         super().save(*args, **kwargs)
 
-    def has_access(self, user: User):
+    def is_shared_with(self, user: User):
         """ Access check
 
         Checks whether a given user has access to this intervention